1. Field of the Invention
This invention relates to motion picture projectors, and more particularly to improvements in a motion picture projector with respect to the film gate structure and to the selection of the various modes of operation by a single control knob.
2. Description of the Prior Art
In the design of a conventional motion picture projector such as those adapted for home use, it is already known to increase the number of functions or modes of operation as including normal motion picture projecting, still picture projecting, slow motion picture projecting, high speed film winding, and high speed film rewinding. Selection of all such functions by use of a single control knob has, however, necessitated a far more complicated operating mechanism. The conventional design features as directed to the provision of as simple a mechanism as possible from the operating and economic standpoints have resulted in successive manipulation of various control members to operate the projector. This constitutes one of the conventional problems.
Another problem that exists with the projection gate structure is that as a projection aperture defining an effective film frame area is formed in a film pressing plate situated between a light source and a film to guide and support the film against a front plate of an over-bored aperture registering with the projection aperture, light rays which pass through the projection aperture at the edge thereof and which impinge on the film are diffusely reflected by the film thickness with a resultant reduction of sharpness at the edge of a viewing area on the projection screen, thus giving an unpleasant impression to the viewer.
To avoid further reduction of such sharpness by the projection gate itself, it is required that the inner edge of the projection aperture must be made sharp. In this case, the surface between the inner and outer edges of the projection aperture is inclined toward the projection light source so that the temperature of the film pressing plate in the vicinity of the projection aperture is increased to a very high level by the heating effect of the radiated rays from the light source and impinging on the pressing plate. For this reason, selection of materials for making the pressing plate has been limited to metal, although thermoplastic resin is very advantageous in manufacturing complicated structure components by extrusion and injection molding techniques. Accordingly, thus far it has been impossible to arrange the film gate mechanism with the projection gate therein so that a single control knob enables all of the various modes of operation.